Dimethyl fumarate is represented by the structure of formula I.

Dimethyl fumarate is indicated for the treatment of patients with relapsing forms of multiple sclerosis. Dimethyl fumarate is marketed under the brand name TECFIDERA® in the United States.
Processes for the preparation of dimethyl fumarate known in the art show presence of impurities such as dimethyl sulfate, monomethyl fumarate, dimethyl maleate in dimethyl fumarate. Use of acid such as sulfuric acid as a catalyst in esterification reaction is also known to pose several problems such as corrosion of reaction vessels, catalyst recovery and waste disposal.
Impurities in dimethyl fumarate or any active pharmaceutical ingredient (API) are undesirable and, in extreme cases, might even be harmful to a patient being treated with a dosage form containing the API.
It is also known in the art that impurities in an API may arise from degradation of the API itself, which is related to the stability of the pure API during storage, and the manufacturing process, including the chemical synthesis. Process impurities include unreacted starting materials, chemical derivatives of impurities contained in starting material, synthetic by-products, and degradation products.
Impurities introduced during commercial manufacturing processes must be limited to very small amounts, and are preferably substantially absent.
Thus there is a need in the art for improved processes for preparing pure dimethyl fumarate, which are more industrially applicable.
The present invention provides commercially viable simple scalable process for the preparation of dimethyl fumarate free of genotoxic impurities.